This invention relates generally as indicated to a welding apparatus and method and more particularly to an exothermic welding apparatus for welding a variety of objects such as electrical conductors in the form of cable, rod, strip, braid, bars, tape and the like, and also in a variety of sizes, as well as a process for economically forming good high ampacity, low resistance electrical connections for such objects.
Exothermic welding has become recognized as a preferred way to form top quality high ampacity, low resistance electrical connections.
Exothermic welded connections are immune to thermal conditions which can cause mechanical and compression joints to become loose or corrode. They are recognized for their durability and longevity. The process fuses together the parts or conductors to provide a molecular bond, with a current carrying capacity equal to that of the conductor. Such connections are widely used in grounding systems enabling the system to operate as a continuous conductor with lower resistivity.
Reusable refractory molds usually made of graphite or the like are widely used with exothermic welding materials to make a wide variety of such high ampacity, low resistance electrical connections. Typical of such molds are those sold under the well-known trademark CADWELD(copyright) by Erico International of Solon, Ohio, U.S.A.
The reusable molds are two or more part molds usually opened and closed and held together by toggle clamps. The mold parts have faces which abut at a parting plane in which are formed recesses forming the various cavities and passages when the parts are clamped together. Typically, the mold parts form a weld chamber, which usually includes a riser which may be the enlarged lower end of a tap hole passage which extends from the top of the mold to the weld chamber.
The parts to be welded enter the weld chamber through sleeving passages which extend from outside the mold to the chamber. Such passages usually extend horizontally.
A crucible normally sits on top of the assembled mold parts. The crucible includes a chamber holding the exothermic material on top of a fusible disk. A sprue or tap hole below the disk communicates with the top of the tap hole of the mold. When a measured and controlled quantity of exothermic material is ignited, it forms molten metal which fuses the disk permitting the molten metal to run downwardly into the weld chamber to weld any parts exposed to the chamber. Any slag forms on top of the weld metal and normally accumulates in the riser. After the weld cools, the mold is disassembled and any slag removed. The molds and crucible are cleaned for reuse.
Such molds can be rather intricate and are not insignificant in cost. More importantly, for each type of connection, a different mold assembly is normally required. These essentially single-use molds create an extremely large number or inventory of molds, and makes the storage, transportation and selective use of such molds both costly and burdensome. While some mold sets may accommodate different size conductors, usually with shims, sleeving or packing around smaller conductors in larger passages, such shims or sleeving contribute to the wear of the molds shortening their useful lives. All of the above contributes to the cost of making such high quality connections. Because of such costs, users and owners may select less expensive but less efficient weld connections and connections of lower quality.
Accordingly, it is desirable to maintain the cost of the apparatus and methods for making such exothermic connections as low as possible. This may ideally be accomplished by eliminating the formed or machined refractory molds surrounding and containing the parts to be joined.
The welding apparatus for forming weld connections includes a base against which is positioned a layered or sandwiched arrangement of refractory batting or gaskets and the parts to be connected. Each batting has a hole intersecting the parts to be connected. A platen is pressed against the layered arrangement to compress the batting around the parts to be connected with the holes in the batting forming the weld chamber. The platen is preferably part of an exothermic welding crucible in which a charge of exothermic material is ignited to form the weld metal to flow through a tap hole into the weld chamber to form the weld connection. Two or more layers of batting may be used depending on the type of connection being formed. After the weld connection is formed, the base and platen crucible are separated and the batting is discarded.
Supporting the base and platen crucible for opening and pressure closing movement is a clamp fixture to which the base and platen are secured. The base is a rectangular block having different patterns on opposite sides and may be flipped over depending on the type of weld connection being made. The fixture supports the base so that the parts may extend diagonally across the block and the batting which is of the same rectangular configuration.
The invention also is a method of forming welded connections, which includes the steps of layering the batting and parts to be welded against the base with the batting layers each having a hole intersecting the parts to be welded, and compressing the layered batting and parts against the base to seal the parts and form a sealed weld chamber. Molten metal is then introduced into the weld chamber and the connection is formed. When released, the batting is discarded.
In this manner, a wide variety of weld connections can be made without special refractory weld chamber mold blocks so widely subject to the inventory and wear problems noted above. In this manner, the same quality weld connections can be made much more easily either in the field or in the shop and at much reduced cost.
To the accomplishment of the foregoing and related ends the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principles of the invention may be employed.